The present invention relates to various articles which contain as a main component a part in which a surface is coated with silver such as optically reflective members used in reflecting mirrors of photocopy machines, indoor and outdoor lighting appliance, automobile headlights, and the like, and to resin composition for coating materials for silver. In more detail, the present invention relates to article having a silver layer in which the anti-disclosing (anti-corrosion) properties are remarkably improved, and to resin composition for coating materials for silver with which it is possible to give to the silver a superior anti-discoloring (anti-corrosion) property.
The present applications based on Japanese patent application No. Hei 10-152751 filed in Japan, the content of which is incorporated hereinto by reference.
Silver ha superior optical properties and electrochemical properties, and has been used as a precious metal from ancient times for decoration, money, eating utensils, electric materials and material for dentistry. In recent times, the use of silver in lighting appliances, photographic industry material for photocopiers and the like liquid crystal displays, semiconductor materials, conductive materials, and aerospace materials has increased rapidly. Silver is used widely as an industrial material.
However, the silver materials which are being put to these uses are extremely unstable chemically, and they react readily with sulfur dioxide gas, hydrogen sulfide, moisture, oxygen and the like in air to generate silver oxide, sulfides of silver, and the like. For this reason, there is the problem that silver surfaces discolor (corrode) to brown or black.
In addition, the discoloration (corrosion) of silver surfaces is further accelerated by high temperature environments, therefore, it has not been possible to use silver in parts such as the reflective mirror of automobile headlights, the temperatures of parts of which exceed 150xc2x0 C. For this reason, aluminum is used in the reflective mirrors of automobile headlights.
However, silver whose surface has been made smooth is very good as a reflective material of light, and has a reflectivity approximately 10% higher than that of an aluminum surface. In addition, in lighting devices, generally, in order to concentrate the light and to match the polarity of the light, or, in order for equalization of luminous and light diffusion, the light is repeatedly reflected, therefore, the difference between the total reflectance of silver and the total reflective of aluminum is even greater. For this reason, the use of silver which is able to give higher lighting illumination from less electrical energy is desired.
On the other hand, as methods for preventing the discoloration (corrosion) of silver, methods of making alloys of silver with other metals such as copper, platinum, palladium, iridium, zinc, tin, and the like. and methods of applying coating material such as epoxy resin or the like to the surface of the silver are known. However, in the former methods, there are problems with the malleability and ductility of silver becoming reduced, and the external appearance of the surfaces being degraded. With the latter methods, the adhesiveness of the coating material with the surface of the silver is unsatisfactory, and the durability of the coating material is unsatisfactory; therefore, it is difficult to prevent discoloration (corrosion) of the surface of the silver over a long period of time.
For this reason, in order for the silver to sufficiently exhibity superior ductility and malleability and obtain a surface having a glossy appearance, a search for a new type of coating material which has improved adhesiveness for the surface of silver and durability without relying on an alloy treatment became necessary.
The inventors of the present invention carried out careful research for a new type of coating material for protecting the surface of silver which had improved adhesiveness for surface of silver and durability, and made a new invention related to a resin composition which can be used in coating materials. In addition, the present inventors have already presented coating materials having improved adhesiveness for the surface of silver and durability in Japanese Patent Application, First Publication No. Hei 06-57198: Japanese Patent Application, First Publication No. Hei 08-245903; Japanese Patent Application, First Publication No. Hei 09-241532: Japanese Patent Application, First Publication No. Hei 10-185572: and Japanese Patent Application, First Publication No. Hei 10-292152.
However, in high temperature environments, there are still situations in which the surface of the silver becomes discolored (corroded) even when these coating materials are used. Furthermore, in uses in which the surface of the silver is exposed to temperatures of around 200xc2x0 C. there is the problem that the coating material turns yellow and hinders the reflecting properties of the silver. For this reason, additional effective strategies for increasing the protective properties for silver surfaces are demanded.
As the result of careful research in view of these circumstances, the present inventors discovered that for the prevention of discoloration (corrosion) of a silver layer laminated as a thin layer onto the surface of a substrate, the protection of the contact surface of the silver layer and the substrate is essential, and that protection of only the reflective surface of the silver is inadequate. Furthermore, they discovered that ingenuity is required in the selection of materials for the formation of a protective layer on the substrate side. In addition, the present inventors discovered that it is possible to obtain a resin composition for coating silver which has superior heat resistance and does not turn yellow even when exposed to temperatures of around 200xc2x0 C. by means of using a multi-functional silicone cross-linked resin having a siloxane component as a main chain.
In more detail, in the article having a silver layer of the present invention,
a first cured coating layer (A) comprising a resin composition in which a resin having anti-corrosion properties for silver and adhesives for both a substrate and silver, or a metal comprising silver as a principal component, is formed on the surface of the substrate;
a silver layer (B) comprising silver or a metal comprising silver as a principal components is formed on this first cured coating layer (A); and
a second cured coating layer (C) having heat resistance and transparency and comprising a resin composition comprising as a principal component at least one type of resin selected from the group consisting of
a silicone acrylic resin (c1),
a silicone alkyd resin (c2), and
a multi-functional silicone cross-linked resin (c3) formed on the silver layer (B). This multi-functional silicone cross-linked resin (c3) has an average compositional formula represented by general formula 1, a number average molecular weight of 500xcx9c1000, and a main chain formed by silicone bonds:
R11Sio(4xe2x88x92m)/2xe2x80x83xe2x80x83(1)
(in the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a substituted phenyl group; and n is a number from 1.2 to 1.4).
By means of above, an article having a silver layer with superior anti-discoloration (anti-corrosion) properties can be obtained.
In addition, it is preferably for the resin which forms the above-mentioned first cured coating layer (A) to be at least one type of resin selected from the group consisting of a silicone acrylic resin (c1), a silicone alkyd resin (c2), and a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by the above-mentioned general formula 1, a number average molecular weight of 100xcx9c1000, and a main china formed by siloxane bonds. Thereby, an article having a silver layer with superior anti-discoloration (anti-corrosion) properties can be obtained.
In addition, it is preferable for the resin which forms the above-mentioned second cured coating layer (C) to be a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by the above-mentioned general formula 1, a number average molecular weight 500xcx9c1000, and a main chain formed by siloxane bonds. Thereby, it is possible to obtained an article having a silver layer in which the second cured coating layer (C) does not turn yellow even when exposed to temperatures of around 200xc2x0 C.
In addition, the above-mentioned substrate is preferably metal or synthetic resin. Thereby, the article having a silver layer sufficiently exhibits the effects of anti-discoloration (anti-corrosion).
In addition, the above-mentioned silver layer (B) is preferably a thin layer of silver or mainly silver formed by a vacuum deposition method, and ion plating method, or a sputtering method. Thereby, the article having a silver layer sufficiently exhibits the effect of anti-discoloration (anti-corrosion).
In addition, the article having a silver layer of the present invention preferably has a specular glossy surface or reflective surface. Thereby, it is possible to obtain an article having a silver layer suitable for a light reflecting member for a reflecting mirror of a copy machine, indoor or outdoor lighting appliances, and automobile headlights.
In addition, since the article having a silver layer of the present invention sufficiently exhibits the reflectance property of silver, it can be effectively used in reflective mirrors for indoor or outdoor lighting appliances and the reflective mirrors of automobile headlights.
The resin composition for coating materials for silver of the present invention contains a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by general formula 1, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds.
RnSiO(4xe2x88x92n)/2xe2x80x83xe2x80x83(1)
(In the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a substituted pheny group; and n is a number from 1.2 to 1.4. )
Thereby, it is possible to obtain a resin composition for coating materials for silver which has superior heat resistance, gives a superior anti-discoloration (anti-corrosion) property to silver and the film of which does not turn yellow even when exposed to high temperature of around 200xc2x0 C.
In addition, it is preferable for the resin composition for coating materials for silver of the present invention to additionally contain silver deactivators, in particular, complexes of zirconium with carboxylic acid. Thereby, it is possible to obtain a resin composition for coating materials for silver which reliably gives a superior anti-discoloration (anti-corrosion) property to silver.
In addition, it is preferably for the coated silver to be a thin layer of silver or mainly silver formed by a vacuum deposition method, an ion plating method, or a sputtering method. Thereby, the effect of giving an anti-discoloration (anti-corrosion) property to the silver is sufficiently exhibited.
In the following, the various selectable constituent features for practicing the present invention and other matters will be explained in detail.
The second cured coating layer (C) of the article having a silver layer of the present invention has heat resistance and transparency and comprises a resin composition comprising as a principal component at least one type of resin selected from the group consisting of a silicone acrylic resin (c1), a silicone alkyd resin (c2), and a multi-functional silicone cross-linked resin (c3) having an average compositional formula represented by general formula 1, a number average molecular weight of 500xcx9c1000, and a main chain formed by siloxane bonds. (In the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a subtituted phenyl group: and n is a number from 1.2 to 1.4.)
The silicone acrylic resin (c1) used in the present invention has hydrolyzable silyl groups bonded to the acrylic main chain. As the silicone acrylic resin (c1), those which can be cured by forming a siloxane-acrylic copolymer due to selfxe2x80x94crossxe2x80x94linking due to heat or active energy ray can be mentioned.
One of these silicone acrylic resins (c1) can be used independently, or a mixture of two or more of them can be used.
The silicone alkyd resin (c2) used in the present invention is one type of the so-called modified silicone resins in which a silicone resin is modified by an alkyd resin. The silicone alkyd resin (c2) used in the present invention is also called an alkyd resin modified silicone resin and means a resin in which the alkyd resin component and a multi-functional siloxane component (hereinafter simply referred to as silicone component) are copolymerized.
As the alkyd resin component used in the modification, there are types modified by oil or fatty acids; and there are types called oil-free alkyds which have not been modified at all: and either of these types may be used. Oil-free alkyd types also include polyester resin. Any of these can be suitably used.
As the multi-functional siloxane component, silicone resin lower condensates, or monomers such as phenylsiloxiane, methysiloxane, and phenylmethylsiloxane can be used. As the silicone resin lower condensate, phenylmethylsilicone resin lower condensates (phenylmethylpolysiloxane lower condensates) which have many phenyl groups, and which contains functional groups such as methoxy groups, ethoxy groups and hydroxyl groups are suitable; and so called plant-use silicone intermediates or modified-use silicone intermediates can be effectively used. Among these, paint-use silicone intermediates are preferable. As the paint-use silicone intermediates, phenyl alkyl silicone resin lower condensates containing functional groups such as phenyl groups, methoxy groupss, ethoxy groups and hydroxyl groups within the molecule can be mentioned.
This silicone alkyd resin (c2), for example, can be suitably prepared by means of known methods. In addition, as examples of the silicone alkyd resin (c2) whichare commerically avaiable as a pre-made product, polyester resin modified silicone resin, oil-free alkyd resin modified silicone resin, and fatty acid modified alkyd resin modified silicone resin, for example. Beckolite M-6652-60 (manufactured by Dainippon Ink and Chemicals, Inc.) Beckolite M-6650-60 (manufactured by Dainippon Ink and Chemicals, Inc.); Baysilone REsin UD-460M (manufactured by Bayer Ltd.), Baysilone Resin 180 (manufactured by Bayer Ltd.), can be mentioned. As can be seen from the following Embodiments, these are effective from the point of view of practical use, but the silicone alkyd resin (c2) is not limited to these, many others are known and can be appropriately selected and used.
As the a multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds which is used in the present invention, so called paint-use straight silicone resins can be effectively used.
In addition, multi-functional silicone cross-linked resins comprising phenyl groups, methyl groups, or mixtures thereof in side chains are preferable.
As the a multi-functional silicone cross-linked resin (c3) havinga main chain formed by siloxane bonds which is used in the present invention, those having a number average molecular weight in the range of 600 to 800 are particularly preferable.
When the number average molecular weight of the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds is less than 500, the suitability for coating (external appearance) is degraded, and therefore this is undesirable. On the other hand, when the number average molecular weight exceeds 1000, the suitability for coating is degraded, and thermal discoloration becomes extreme, therefore, this is undesirable.
The degree of siloxane cross-linking in the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds used in the present invention is expressed by R/Si (the average number of organic groups bonded to a single silicone atom, and corresponds to n) in the general formula (1). A degree of siloxane cross-linking within the range of 1.2 to 1.4 can be suitably used.
When R/Si is less than 1.2, the coating film becomes brittle, and cracks are generated in the coating film due to heat. When R/Si exceeds 1.4, adhesiveness with respect to silver is reduced, the gas barrier property and the like of the coating film are degraded, and it is not possible to prevent yellowing of the coating film due to heat, therefore, this is not desirable.
This multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds can be suitably produced using known methods, for example.
In more detail, it can be produced by mixing one or more of various chlorosilane compounds, and carrying out hydrolysis followed by condensation.
In addition, as examples of the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds which are commercially available as pre-made products, there are straight silicone resin SH 804 and SR 2400 (manufactured by Dow Corning Toray Silicone Co., Ltd.): TSR 144 (manufactured by Toshiba Silicone Co., Ltd.): and KR 311 (Shin-Etsu Chemical Co., Ltd.). As can be seen from the following Examples, these are effective from the point of view of practical use, but the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds is not limited to these, many others are known can be appropriately selected and used.
In the present invention, by means of using this type of multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds, it is possible for the first time to form a reflecting mirror for an automobile head light which can be exposed to high temperatures of 200xc2x0 C. or greater using silver.
In addition, when these types of heat resistant resin are used in the coating layer, they can be used independently or together, and they can be selected according to requirements for anti-corrosion properties, heat resistance, photo resistance and heat resistance of the substrate.
In more detail, the upper limit for heat resistance is approximately 160xc2x0 C. (approximately 180xc2x0 C. for short term use of about 100 hours or less) for the silicone acrylic resin (c1); approximately 180xc2x0 C. (approximately 200xc2x0 C. for short term use of about 100 hours or less) for the silicone alkyd resin (c2); and approximately 230xc2x0 C. for the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds.
Each of these resins (c1), (c2), and (c3) has superior adhesiveness for both silver or metals comprising mainly silver and for the substrate, and they are superior in anti-corrosion properties for silver, therefore, they are effective for formation of the first cured coating layer (A) and the second cured coating layer (C). However, there are differences to a certain degree in anti-corrosion properties and heat resistance in these cured coatings, therefore, by selecting and using them based on the required properties for the desired product, those properties can be effectively displayed.
However, in order, anti-corrosion properties is best in the silicone acrylic resin (cl), followed by the silicone alkyd resin (c2), followed by the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds.
In addition, the order for photo resistance is that the silicon acrylic resin (c1) is better than the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds, which is better than the silicone alkyd resin (c2).
In addition, the baking temperature for the purpose of forming the cured coating of each of the resins is approximately 130xc2x0 C. for the silicone acrylic resin (c1), approximately 180xc2x0 C. for the silicone alkyd resin (c2), and approximately 200xc2x0 C. for the multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds. Consequently, the selective range is regulated by the heat resistance of the substrate.
In the article having a silver layer of the present invention, at least one resin selected from the group consisting of a silicone acrylic resin (c1), a silicone alkyd resin (c2), and a multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds is effective as the resin which forms the first cured coating layer (A). From among these, in consideration of adhesiveness for the substrate and anti-corrosion properties of silver or metals comprising mainly silver, the silicon alkyd resin (c2) is the most effective. However, the resin is not particularly limited to these.
Moreover, when the first cured coating layer (A) is absent, it is not possible to obtain sufficient adhesiveness between the silver layer (B) comprising silver or a metal comprising mainly silver and the substrate, or anti-corrosion properties of the silver layer (B); and in addition, when the silver layer (B) is a thin film of silver or mainly silver formed by means of a vacuum deposition method, and ion plating method or a sputtering method, it is not possible to obtain satisfactory mirror surface properties. In addition, even when the second cured coating layer (C) is formed on silver layer (B), it is difficult to prevent corrosion from the rear surface of the silver layer (B). Due to this point as well, the formation of a first cured coating layer (A) is important, and depending on the selection of the materials therefore, the results therefrom are even more remarkable.
For the articles having a silver layer of the present invention, as the method of forming the silver layer (B) comprising silver or mainly silver by deposition, known methods of vacuum deposition methods, ion plating methods, or sputtering methods can be suitably used. Here, the amount of silver within the metal comprising mainly silver which forms the silver layer (B) is not particularly limited. For example, amounts at which the effects of the present invention are particularly displayed are 80% by weight or greater, and at which the effects are even further displayed are 95% by weight or greater.
Next, the resin composition for coating materials or silver of the present invention will be explained. The resin composition for coating materials for silver of the present invention contains a multi-functional silicone cross-linked resin (c3) having a main chain formed by siloxane bonds which has an average compositional formula represented by general formula 1, and a number average molecular weight of 500xcx9c1000.
RnSiO4xe2x88x92n)/2xe2x80x83xe2x80x83(1)
(In the formula, R is a hydrogen atom, a lower alkyl group, a phenyl group, or a substituted phenyl group; and n is a number from 1.2 to 1.4. )
As the metal deactivator used in the present invention, for example, complexes of zirconium with lower fatty acids (carboxylic acids) having benzoyl groups substituted with lower alky groups such as a complex of zirconium with 4-methyl-xcex3-oxo-benzene-butanoic acid; and dicarboxylic acid addition derivatives of mercaptobenzothiazol such as (2-benzothiazorylthio)-succinic acid can be mentioned. These metal deactivators may be used independently or mixtures of two or more of them may be used.
In addition, in accordance with need, known additives such as curing catalysts, solvents, leveling agents, coupling agents, anti-foaming agents, flatting agents. UV absorber, antioxidants, and the like can be added to the resin composition for coating materials for silver of the present invention.
As the curing catalysts used in accordance with need, metallic soaps and metal alcoholates, such as tetra-n-butoxytitanium, and zinc octylate can be mentioned. These curing catalysts may be used independently or mixtures of two or more of them may be used.
As the solvents used in accordance with need, aromatic hydrocarbons such as toluene and xylene; alcohols such as methanol, ethanol, and isopropyl alcohol: esters such as butyl acetate, ethyl cellosolve, methyl cellosolve, cellosolve acetate: and ketones such as methylethylketone, methylisobutylketone and cylohexanone can be mentioned. These solvents may be used independently or mixtures of two or more of them may be used.
As specific examples of the coupling agents used in accordance with need, aluminum type coupling agents, titanate type coupling agents, and silane type coupling agents, such as vinyltris(xcex2-methoxyethoxy)silane, xcex3-glycidoxyproxytrimethoxysilane, tetra(2,2xe2x80x2-diaryloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, acetoalkyoxyaluminum, and diisopropylate can be mentioned. These coupling agents may be used independently or mixtures of two or more of them may be used.
As the coating method for the resin composition for coating materials for silver of the present invention, for example, there are flow coater method, spray method, dipping method ant the like, and the method may be appropriately selected in accordance with the shape of the article being coated. A coating thickness of 3 to 30 xcexcm is suitable, but within this range, a thickness of 8 to 15 xcexcm is preferably from the point view of anti-discoloration (anti-corrosion) properties and durability.
As applications for the articles having a silver layer of the present invention, materials for lighting appliances, electrical uses such as photocopy machines, semi-conductor materials, aerospace materials and the like, and general industrial materials can be mentioned. In particular, since the articles of the present invention are superior in anti-discoloration (anti-corrosion) properties, and are able to sufficiently exhibit the light reflecting properties of silver, they are suitable for applications in which even small amounts of discoloration (corrosion) will have a large impact such as in automobile headlights, lighting appliances for indoor and outdoor use in which the thin film of silver is formed into a light reflecting surface using deposition. When the article having a silver layer of the present invention is used as the reflecting mirror in automobile headlights, the illuminance of the automobile headlights is increased by 15% when compared to conventional aluminum. In addition, when the article having a silver layer of the present invention is used as the reflecting mirror in indoor lighting appliances, the illuminance of the indoor lighting appliance is increased 30% to 50% when compared with conventional aluminum.
In addition, the resin composition for coating materials for silver of the present invention can effectively be used in these types of articles.
In addition, when the resin composition for coating materials for silver of the present invention is used on a thin layer of silver, and in particular on a surface of a deposited silver, superior effects are exhibited as mentioned above, and when used on solid silver, the effects of the present invention as a surface coating agent therefor are also remarkably exhibited.